The present invention relates to semiconductor lasers. In particular, the present invention relates to single-mode, high-power, wide-stripe, diode lasers.
Diode lasers typically include a multilayer laser structure that provides an injection of electrons and holes in an active region. Light is generated when the electrons and holes recombine in the active region.
Diodes with a narrow lateral waveguide width (typically 1-5 xcexcm) can emit a single spatial mode, but are limited in power due to the small volume of the active region necessary for a single-mode laser. Lasers that use an active region of lateral width of 100-200 xcexcm can operate with optical power higher than the narrow-stripe lasers discussed above. Unfortunately, these lasers tend to generate multimode radiation. In other words, there is in the known arts, typically a trade off between the amount of power generated by a laser and the number of modes emitted by the laser; reducing the number of output modes also reduces the available optical output power.
The available optical power for diode lasers is also limited by the optical losses within the optical cavity. During the last several years, considerable improvement in output powers has been obtained for wide-stripe diode lasers due to the application of a new concept called the broadened wave guide version of separate confinement heterostructure quantum well diode lasers. Analysis of this design shows higher power output and better reliability than in conventional lasers. This is due to reduced internal losses, and to reduced optical power density in both the quantum well active region and laser facets.
The broadened waveguide concept has been successfully applied to the fabrication of different types of diode lasers with wavelengths in the range from 0.8 to 2 xcexcm. For example, for a 0.97 xcexcm wavelength Al-free laser with a 100 xcexcm aperture, continuous wavelength powers of 8-10 W, and quasi-continuous-wavelength powers of 13-14 W, were obtained from devices prepared by both Molecular Beam Epitaxy and Metal Organic Chemical Vapor Deposition. These record output powers directly result from very low internal losses in broadened-waveguide lasers. This, in turn, leads to the opportunity to use devices with cavity length as long as 2-4 mm.
Both conventional wide-stripe lasers and wide-striped broadened-waveguide lasers, however, tend to exhibit lateral and longitudinal multimode behavior at currents well above threshold, and their spectra and lateral far fields become dramatically broadened and unstable. Additionally, these lasers, as well as conventional wide stripes lasers, typically operate with filaments that are self focusing and self sustaining, and this can lead to the laser""s degradation.
Thus, a need exists to provide a high-power, single-spatial-mode laser that minimizes these nonlinear effects, and that minimizes their consequential problems.
To alleviate the problems inherent in high-power semiconductor lasers, and to satisfy the need for a high-power, single-mode laser, one embodiment of the present invention use a wide-stripe, angled distributed-Bragg-reflector laser geometry. For the purposes of the present invention, the term xe2x80x9cwide stripexe2x80x9d encompasses stripes that are at least as wide as approximately 20 microns.
In one embodiment of the present invention, a diode laser comprises a semiconductor body having a current-pumped stripe region, an output surface and a reflection surface. The reflection surface can be a distributed Bragg reflector grating disposed in the semiconductor body at a non-parallel angle to the output surface. The output surface and the reflection surface define a laser cavity that substantially contains the current-pumped stripe region.